The present invention relates to processes for the preparation of 1,5-diarylpyrazoles, and chemical intermediates that serve as useful intermediates in the preparation of 1,5-diarylpyrazoles. 1,5-Diarylpyrazoles are particularly useful in the treatment of inflammation and inflammation-related disorders, including arthritis.
Selective inhibitors of cyclooxygenase-2 (COX-2) have demonstrated effective anti-inflammatory activity with reduced gastrointestinal side effects, as compared to other antiinflammatory agents, e.g., NSAIDs, that inhibit both the constitutive form of cyclooxygenase (COX-1), and the inducible form of the enzyme, COX-2. A particularly effective structural class of selective COX-2 inhibitors are the 1,5-diarylpyrazoles. For example, the compound, 4-[5-(4-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonamide (celecoxib(copyright)) has been approved by the Food and Drug Administration for the treatment of rheumatoid arthritis and osteoarthritis.
Penning et al. (J. Med. Chem. 1997, 40, 1347-1365) discloses that 1,5-diarylpyrazoles can be prepared by condensation of 1,3-dicarbonyl adducts with aryl hydrazines. The 1,3-dicarbonyl adducts can be prepared by Claisen condensations of aryl methyl ketones with carboxylic acid esters. In an alternate preparation, the 1,5-diarylpyrazoles can be synthesized by epoxidation of xcex2-aryl-xcex1,xcex2-unsaturated ketones, followed by condensation of the resulting epoxides with arylhydrazines.
In one embodiment, the invention relates to a process for preparing a compound of the formula 
R1, R3 and R4 are independently selected from the group consisting of hydrogen; halogen; preferably fluoro, chloro, bromo or iodo; hydroxyl; nitro; C1 to C6 alkyl, preferably C1 to C3 alkyl; C1 to C6 alkoxy, preferably C1 to C3 alkoxy, more preferably methoxy; carboxy; C1-C6 trihaloalkyl, preferably trihalomethyl, more preferably trifluoromethyl; and cyano.
R2 is amino; or lower alkyl, preferably C1 to C3 alkyl.
In preferred aspects, the invention relates to the process for preparing a compound having the formula 
Preferably R1 is methyl, particularly where R2 is amino.
The process includes the step of condensing an alkyne of formula 
with a phenyl hydrazine of the formula 
or a salt thereof.
In some embodiments, the alkyne of the formula 3 is prepared by:
(i) adding bromine to a compound of formula 
and
(ii) contacting the product of step (i) with a base.
In one embodiment, the compound of the formula 2 can be prepared by treating a compound of the formula 
with trimethyl(trifluoromethyl)silane in the presence of cesium fluoride.
In an alternative embodiment, the compound of formula 3 can be prepared by a process that includes:
(i) contacting a phenylacetylene of the formula 
with carbon monoxide, oxygen, and methanol, in the presence of a palladium (II) catalyst to provide a propargylic ester of the formula 
and
(ii) treating the propargylic ester of the formula 9 with trimethyl(trifluoromethyl)silane in the presence of cesium fluoride to give the compound of formula 3.
In another aspect, the invention relates to a compound of the formula 
R1, R3 and R4 are independently selected from the group consisting of hydrogen; halogen; preferably fluoro, chloro, bromo or iodo; hydroxyl; nitro; C1 to C6 alkyl, preferably C1 to C3 alkyl; C1 to C6 alkoxy, preferably C1 to C3 alkoxy, more preferably methoxy; carboxy; C1-C6 trihaloalkyl, preferably trihalomethyl, more preferably trifluoromethyl; and cyano.
In a preferred embodiment, the compound has the formula 
wherein R1 is lower alkyl, preferably methyl.
The following terms shall have, for the purposes of this application, the respective meanings set forth below.
xe2x80x9clower alkoxyxe2x80x9d shall include linear or branched C1 to C6 alkoxy groups, unless otherwise specified.
xe2x80x9clower alkylxe2x80x9d shall include linear or branched C1 to C6 alkyl groups, unless otherwise specified.
In accordance with the present invention, novel processes and synthetic intermediates for the preparation of 1,5-diarylpyrazoles are provided. The processes of the invention have been developed from readily available and inexpensive starting materials. Furthermore, the processes provide high yields of 1,5-diarylpyrazoles, and simplify isolation and purification steps. 
One embodiment of the invention is depicted in Scheme 1, wherein R1-R4 are as described above for the compound of formula 1, and Y is a halide, preferably chloride. An alkyne of the formula 3, is condensed with a phenyl hydrazine compound of the formula 4 to provide a 1,5-diaryl-3-trifluoromethylpyrazole of the formula 1. Preferably, the phenyl hydrazine compound of the formula 4 is provided as a salt, e.g., a hydrochloride salt. The reaction can be completed in a protic solvent such as ethanol, n-propanol, isopropanol, butanol or acetic acid at an elevated temperature, e.g. ethanol at reflux. Typically a slight excess of phenyl hydrazine is used, from about 1.05 to about 1.3 molar equivalents. The reaction provides high regioselectivity with respect to the ratio of products obtained of the 1,5-diaryl type (i.e. compound of the formula 1) to the 1,3-diaryl type (not shown). Typically, the ratio of the desired 1,5-diaryl pyrazole to the undesired 1,3-isomer is greater than 9 to 1. Purification of the compound of formula 1 can be conveniently carried out by recrystallization from alcohol solvents, e.g., ethanol.
Various acid addition salts of the compound of the formula 1 can be prepared by treatment with an organic or inorganic acid. Preferably, the acid addition salts formed are pharmaceutically acceptable salts, such as those described in U.S. Pat. No. 5,563,165, the disclosure of which is herein incorporated by reference. Suitable base addition salts of the compound of formula 1, wherein the phenyl group at the 5-position of the pyrazole ring incorporates a carboxy or hydroxyl substituent. Base addition salts include metallic addition salts, e.g, sodium, potassium, and organic base addition salts, e.g, organic amines. Other pharmaceutically acceptable acid addition salts are detailed in U.S. Pat. No. 5,563,165.
The phenyl hydrazine compound of the formula 4 can be prepared from substituted anilines of the formula 11, wherein R2 is amino or lower alkyl as shown in Scheme 2. Preferably, the aniline contains the amidosulfonyl or alkylsulfonyl group in the para position as shown in the structural formula for 11. A diazonium salt is formed from the substituted aniline by treatment with nitrous acid (e.g., formed from hydrochloric acid and sodium nitrite). For example, an aqueous mixture of sulfanilamide and hydrochloric acid is treated with a solution of sodium nitrite at temperatures below about 5xc2x0 C. to form the corresponding diazonium salt. The cold diazonium salt is then treated with a reducing agent, e.g., stannous chloride, to provide the substituted phenyl hydrazine compound. It will be appreciated that alternative well-known preparations of phenyl hydrazine compounds can also be used, for example, preparation from phenyl halides by nucleophilic displacement by hydrazine. 
The alkyne of the formula 3 can be prepared by synthetic methods that are depicted in Schemes 3 and 4. In one embodiment, the alkyne of the formula 3 is obtained from an xcex1,xcex2-unsaturated ketone precursor, the compound of formula 2 (Scheme 3). The compound of formula 2, for example, is first treated with bromine in a suitable inert organic solvent, e.g. chloroform, at room temperature for a sufficient amount of time to form an xcex1,xcex2-dibromo intermediate. The crude product obtained from the bromination reaction is subsequently treated with a base such an alkali metal hydroxide, e.g., potassium, sodium, or lithium hydroxide, to effect elimination of HBr and provide the alkyne of formula 3. The alkyne of the formula 3 can be further purified by, for example, recrystallization from suitable solvents, e.g., alcohols, when the compound is a solid. Alternatively, the compound of the formula 3 can be purified by, for example, chromatography. 
In one embodiment, the compound of formula 2 can be obtained by electrophilic addition of a vinylogous ester, 4-ethoxy-1,1,1-trifluoro-3-buten-2-one, to the substituted phenyl compound of the formula 8. For example, toluene (R1=methyl) can be treated with an equimolar amount of 4-ethoxy-1,1,1-trifluoro-3-buten-2-one in a suitable inert solvent, e.g., dichloromethane, to provide 1,1,1-trifluoro-4-(4-methylphenyl)-3-buten-2-one. Typically, a catalytic amount, e.g.  less than 10 mole %, of a Lewis acid, e.g., zinc chloride, is added to the reaction mixture to catalyze the addition.
In this embodiment and an all other embodiments suitable protecting groups, well known in the art, can be used, where necessary, to protect various phenyl substituents (i.e., R1, R3 and R4), which are then removed later in the synthesis by known methods. Thus, for example, a hydroxyl moiety can be protected as a methyl or silyl ether. Similarly, a carboxy moiety can be protected as an ester if necessary, which can be hydrolyzed in a later in a later synthetic step.
In another embodiment, the compound of formula 2 is obtained from a cinnamic acid ester of the formula 5, by treatment with trimethyl(1,1,1-trifluoromethyl)silane and cesium fluoride (Scheme 3). The reaction is carried out neat, or in an inert organic solvent, e.g, dichloromethane, tetrahydrofuran, at a temperature of about 15 to about 30xc2x0 C. The cinnamic acid ester can be obtained from a Heck coupling of a halophenyl compound of the formula 6 (wherein X is Cl, Br, or I, preferably Br or I) with an alkyl acrylate of the formula 7. The reaction mixture includes a base, e.g., potassium carbonate, and a palladium catalyst. Palladium catalysts for the Heck reaction are well-known and include palladium(II) acetate. A stabilizing ligand for the palladium such as triphenylphosphine can be included in the reaction mixture, include A preferred catalyst is Pdxe2x80x94Cu-Mont. K-10 (clay). The reaction is typically carried out in a dipolar aprotic solvent e.g., dimethylfornamide, at temperatures of about 100 to about 160xc2x0 C. The Heck procedure permits regioselective coupling of the alkyl acrylate group on to the phenyl ring. This procedure is particularly advantageous for compounds wherein the electrophilic addition of the vinylogous ester to the phenyl precursors 8 described above leads to unfavorable mixtures of regioisomers in the product.
In another embodiment of the invention, the alkyne of the formula 3 is obtained by treatment of a propargylic ester of the formula 9, with trimethyl(1,1,1-trifluoromethyl)silane and cesium fluoride (Scheme 4). Here again, the reaction is carried out neat, or in an inert organic solvent, e.g, dichloromethane, tetrahydrofuran, at a temperature of about 15 to about 30xc2x0 C. 
The propargylic ester of the formula 9 can be obtained from a phenylacetylene having the formula 10, wherein R1 is as described above. The reaction is catalyzed by a palladium (II) catalyst, e.g., palladium (II) acetate, in a methanol at a temperature of about 15xc2x0 C. to about 40xc2x0 C. Preferably, the reaction catalyzed by a palladium (II) catalyst (e.g., palladium (II) acetate), molybdovanadophosphate (NPMoV), and chlorohydroquinone (HQ-Cl).
In another embodiment, the propargylic ester of the formula 9, may be obtained by formation of the corresponding anion of the alkyne having the formula 10, with a strong base, e.g., n-butyllithium, lithium diisopropylamide, lithium hexamethyl-disilazide, and addition of the anion to an activated derivative of trifluoracetic acid, e.g, trifluoroacetyl chloride, trifluoroacetic anhydride.